The invention relates to improvements in apparatus for simultaneously pumping two or more different liquids, such as paints, lacquers, resins and/or others More particularly, the invention relates to improvements in apparatus of the type wherein several individual pumps are operated alternatingly, i.e., one of the pumps displace a liquid while the other pump is in the process of drawing liquid from a source and vice versa
German Offenlegungsschrift No. 30 31 067 of Clements discloses a pumping apparatus with two discrete diaphragm pumps wherein the plungers which actuate the membrane-like pumping elements are reciprocated in working cylinders by the adjacent ends of the piston rod of a pneumatic axial piston motor or by an eccentric disposed between two rod-like members each of which carries one of the plungers. One of the working cylinders is accessible and can be adjusted axially at the exposed front side of the apparatus in order to change the capacity (rate of delivery) of the respective pump in response to shifting of an opening or port which serves to connect the respective cylinder with a reservoir for a supply of hydraulic operating fluid. This results in a change of the ratio of the two liquids which are delivered by the diaphragm pumps. If such an adjusting device is provided, the membrane of the corresponding diaphragm pump cannot be mounted in a position of coaxiality with the respective plunger; the housing of the apparatus is then provided with a lateral extension for such membrane
Each of the diaphragm pumps serves for delivery of a different liquid, e.g., a paint, a resin or a lacquer. The ratio of liquids can be altered in the aforementioned way, i.e., by adjusting the cylinder for the plunger which actuates the pumping element (membrane) in one of the diaphragm pumps. The two pumps operate alternatingly, i.e., one of the pumps delivers a metered quantity of a first liquid while the other pump is in the process of drawing a metered quantity of a second liquid from the respective source, and vice versa. In other words, metered quantities of first liquid are delivered to a consumer (e.g., to a spraying device) during spaced-apart intervals of time which alternate with the intervals of delivery of metered quantities of the second liquid. Such mode of operation is not satisfactory for a number of purposes, e.g., for applying a mixture of two liquids to a surface which is to be coated and/or otherwise treated. Therefore, metered quantities of the two liquids must be delivered first into a mixing vessel in order to ensure that the object which is to be provided with a coat containing the two liquids will invariably receive a proper mixture of liquids. Otherwise, the composition of a paint containing several components would be unsatisfactory, or the hardening or setting of a lacquer wold not progress in the desired way.
Apparatus for simultaneous pumping of two liquids, each by a single pump, are further disclosed in U.S. Pat. No. 3,330,211 to Faro et al. and in British Pat. No. 1,202,877 to Horsford et al. German Offenlegungsschrift No. 32 33 987 of Roser discloses an apparatus wherein several diaphragm pumps are installed in a common housing. U.S. Pat. No. 3,499,387 to Zippel discloses a plastic injection machine wherein four liquid plastic material components are delivered by four discrete pumps. German Offenlegungsschrift No. 14 53 597 of Burgert discloses an adjustable diaphragm pump, and German Auslegeschrift No. 15 28 599 discloses a plunger which carries a seal so as to reduce leakage of conveyed fluid at elevated pressures